Gasification of carbonaceous solids



Oct. 6, 1953 J. A. PHINNEY GASIF'ICATION OF CARBONACEOUS SOLIDS E'iledFeb. 2l, 1950 Patented Oct. 6, 1953 GASIFICATION 0F CARBONACEOUS SOLIDSJohn A. Phinney, to Pittsburgh Pittsburgh, Pa.,

Mount Lebanon, Pa., assignor Consolidation Coal Company, a corporationof Pennsylvania Application February 21, 1950, Serial No. 145,374

1 claim. 1

This invention relates to the gasification of carbonaceous solids and,more particularly, to the conversion of finely divided carbonaceoussolid fuels to carbon monoxide and hydrogen in a iiuidized steam-carbonreaction zone.

Operation o1 gasification systems employing a iluidized bed of carbonthrough which steam is passed at reaction temperature has demonstrated avery high rate of entrainment of solid nes in the eiuent gases from theluidized bed. As high as 1600 pounds of nes per hour per square foot ofreactor cross-section (or 300 pounds per 1000 cubic feet of reactorefliuent gas) have been observed. These entrained fines have beenrecirculated through the fluidized bed in an attempt to gasify them.However, such recirculation does not appreciably iniiuence the analysisof the uidized material remaining in the dense phase, thus demonstratingthat the nes are not retained in the bed and accordingly not gasied.

The primary object of this invention is to provide a uidized system forgasifying finely divided carbonaceous solid fuels wherein the carbon fedto the system is substantially completely gasied.

In accordance with my invention, the solid fines entrained by theeiiiuent gases from a fluidized steam-carbon reaction zone areconducted, along with coarser solids withdrawn directly from theiiuidized bed, to a uidized combustion zone. Here the solids arecompletely burned, and the coarse ash is rejected from the system. Atleast a portion of the hot fine sized ash entrained in the eiiluent fluegases from the combustion zone is recirculated through the steam-carbonreaction zone to supply the necessary heat thereto by direct heatexchange with the solids in the uidized bed. The particle size of therecirculated ash is regulated to insure its entrainment by the uidizinggas in the steam-carbon reaction zone. Thus heating of the latter zoneis accomplished without build-up of the ash content. By means of thissystem, it is possible to completely consume the carbon fed to thegasification system, thereby eliminating the problems associated withungasied fines and high ash bed solids.

For a better understanding of my invention, its objects and advantages,reference should be had to the following detailed description and to lthe attached drawing in which is illustrated,

partly diagramma-tically and partly in section,

a preferred embodiment of my invention.

Referring specically to the drawing for a description of the apparatusin which the pre- I ferred embodiment is practiced and also itsoperation, numeral I0 designates a steam-carbon reaction vessel adaptedto confine a fiuidized bed of carbon II. solid fuel from a hopper I2 isfed through a conduit I4 into a conduit I 6 through which sufiicientsteam is circulated to pick up the fuel and carry it into the vessel I0.The balance of the steam required for reaction with the carbon issupplied through a conduit I8 which communicates with the bottom ofvessel I 0. Heat is provided for the steam-carbon reaction in a mannerto be described later. However, if desired, the steam may be preheatedbefore introduction in vessel I0 by a boiler 20 arranged in heatexchange with conduit I 8.

The size of the fuel particles and the superficial velocity of the totalsteam are selected to give iiuidizing conditions in a manner well knownin the art. However, the solid particles consist of a wide range ofsizes as is generally produced upon once through grinding of the fuel toa iinely divided state. Consequently, the gas velocity required toproperly fluidize the coarser particles is suiiiciently high to produceentrainment of the smaller particles.

The eiiiuent gases and entrained solid fines are discharged overheadfrom vessel l0 through a conduit 22 to a cyclone separator 24. Theproduct gas is recovered through conduit 26 and its sensible heattransferred, if desired, to a Waste heat boiler 28. The fines aredropped 'from the separator through a, conduit 30 to a conduit 32 andpicked up by a stream of air circulating therethrough. At the same time,coarse solids from the iiuidized bed II in vessel I0 are withdrawnthrough a draw-ofi line 34 and fed into the same air conduit 32 foradmixture with the overhead fines. This mixture of solids is conductedto a combustion vessel 36 wherein a fluidized bed 31 of the solids ismaintained by thev air. Because of the rapid rate of reaction of carbonand oxygen, a substantial portion or all of the combustion of the solidswill occur in the line 32. The superficial velocity of the airv through-vessel 36 is so chosen that the particle size of the ash entrained inthe effluent gases is small enough to insure entrainment in vessel I0.Coarse ash is discharged from the bed in vessel 36 through a draw-01Tconduit 38. For example, for a range of particle size in bed II invessel I0 of between 35 and 200- mesh and a fluidizing gas velocity of1.0 foot per second, the fluidizing gas velocity in vessel 36 should be0.7 or if the fluidizing velocity in vessel I0 is 2.0

Finely divided carbonaceous 3 feet/second the fluidizing gas velocity invessel 36 should be 1.7 feet/second.

The eiliuent flue gases and entrained ash are discharged overhead fromvessel 36 through a conduit 40 to a cyclone separator 42. The hot solidfree gas is then conveyed through a conduit 44 in heat exchange relationwith the air line 32 to preheat the air. The fine ash particles aredropped through a conduit 46 to the steam line I8. Net fine ash isrejected from the system through a draw-off conduit 48.

The fine ash is picked up by steam in conduit I8, and recirculated tothe fluidized bed Il in vessel l0. The amount of ash recirculated isregulated to supply the heat required to maintain the endothermicsteam-carbon reaction in vessel I0. As previously indicated, theparticle size of the recirculated ash is such that its entrainment inthe effluentgases in vessel I is assured. Thus, While the ash furnishedthe heat required, it does not alter the analysis of the material in thebed in vessel I0 by build-up of ash.

In the preferred embodiment described above, the particle size of therecirculated fine ash is controlled to insure its entrainment in thefluidizing gases in the gasification vessel by regulating thesuperficial velocity of the oxidizing gas in the combustion zone. Thesame result may be secured by substituting a suitably7 designed cyclonefor vessel 31 in the combustion zone to reject particles which are toolarge for recirculation to Vessel Il. The desired ner particles arethereafter separated in cyclone 42.

The following example is given by Way of illustration only. Acarbonaceous solid fuel of the following typical screen analysis foriiuidization 'is fed to the gasification zone operating at 17 00 F.

The carbon and ash contents of this feed are 78.3 and 13.4 Weightpercent respectively. For every 100 pounds of fresh feed, 4050 pounds ofne ash from the combustion zone operating at 1950 F. are also fed to thegasier, entrained in 180 pounds of steam previously preheated to 1400DF.. by heat exchange. With an exit gas velocity of about 1.5feet/second, the recirculated ash rines are immediately entrained fromthe fluid bed, together with the vmajority of the fresh feed solids of asize consist finer than 200 mesh (ca pounds/100 pounds of fresh feed).The ash content of the nuid bed is dictated only by the entrainedcoarser particles, and in this example is maintained at about 75% byproper balance of feed rate and steam carbon reaction rate throughproper control of reaction temperature, bed inventory, and steamconversion.

The entrained ash nes together with net fines from the fresh feed arecollected at reaction temperature in the cyclone separator and recycledto the combustion zone by entrainment in preheated combustion air. Theaverage carbon content of this stream is about 0.5-2.0%. Product gasespass to subsequent heat exchange and cooling equipment. The coarserparticles,

mesh 17.0

constituting the net reject from the gasification vessel fiuid bed andcontaining 25% carbon, are also carried to the combustion zone incombustion air. Combustion of the carbon in both the net fines and theash reject from the gasification zone (13 pounds/100 pounds feed) raisedthe average temperature in the combustion zone to 1950 F. Separation ofthe ycoarse and fine ash is accomplished by either entrainment orcyclonic action, While final separation of fines from flue gas iscarried out at 1950 F. in subsequent cyclones. Net coarse ash and netfine ash are rejected from the system, the remaining fine ash beingrecycled to the gasification section as described above.

According to the provisions of the patent statutes, I have explained theprinciple, preferred construction, and mode of operation oi' myinvention and have illustrated and described What I now consider torepresent its best embodiment. However, I desire to have it 'understoodthat, Within the scope of the appended claim, the invention may bepracticed otherwiseA than as specifically illustrated and described.

I claim:

The method of gasifying nely divided carbonaceous solid fuel whichcomprises continuously supplying finely divided carbonaceous solid fuelof different particle sizes to a confined gasiiieation zone to therebyestablish and maintain a bed of solids in said zone. passing steamupwardly through said bed at a velocity sufficient to maintain thesolids as a suspended dense turbulent phase superimposed by a dilutesolids phase in said gasification zone, continuously sup-v plying hotsubstantially carbon-free ash fines derived from said fuel to saidgasification zone, passing said ash fines upwardly through said densephase in said gasication zone and into said dilute phase, the particlesize range of said ash fines being such that substantially all of saidash is carried into said dilute phase by the efliuent gas from saiddense phase, separating said ash nes and any entrained carbonaceousfines from said dilute phase, withdrawing solids having an averagecarbon content corresponding to that of said dense phase directly fromsaid gasification zone and combining said solids with said separatediines outside of said gasification zone, passing said combined solids toa combustion zone, circulating an oxidizing gas in contact With `saidsolids in said combustion zone under conditions such that thetemperature of the combustion zone is maintained above that of saidgasification zone and such that said solids are reduced to asubstantially carbon-free state, separating from the ash produced insaid combustion zone a portion having a particle size range.corresponding to that of the first mentioned ash fines, recycling thatportion only to said gasification zone, and recovering the gaseousproducts from said gasification zone.

JOHN A. PHINNEY.

References Cited in the le of this patent UNITED STATES PATENTS NumberName Date 2,429,127 Graham et al Oct. 14, 1947 2,436,938 Scharmann et alMar. 2, 1948 2,482,187 Johnson Sept. 20, 1949 2,560,403 Arveson July 10,1951 FOREIGN PATENTS Number Country Date 600,326 Great Britain Apr. 6,1948

